920 Appendix III.
float falls, valve G moves downward, admitting steam to top of H,
which thus opens feed valve still wider. Eut the movement of H
downward also cuts off steam supply at G, and all is quiet again
with increased rate of feed. Conversely, if the feed be too rapid
the float rises, lifting G, and, the top of H being thus opened to
exhaust'M, the unbalanced steam pressure at bottom causes H
to rise and slightly close the feed valve. Also the act of rising
once more cuts off G and restores equilibrium with a decreased
rate of feed.
To raise the water level permanently, shut off steam at c and
open the blow-out cock N, thus flooding the float with water.
Next, turn the screw P till pointer Q shows level required.
Keeping N still open, re-open the cock at c, and the water level
falls, the extra water in the float being blown out, until the steam
freely flows through bottom end of pipe R, when the definite
weight of water remaining at s will keep the float at the exact
level indicated by Q. In lowering the water level the flooding
need not be done, for when R is depressed to the proper
position, the superfluous water may be removed at s by blowing
through. The hand gear at T is for testing the freedom of the
float. (Seep. 1063.)
| ? | CHAPTER VIII
\\< P. 361. Stress.—It is well to warn students of the various
if; I uses to which this word has been put. Most authorities agree in
i'f> applying it generally to the state of the molecules; but while
|,4 | some also take it to mean unit stress or stress per square inch,
! |! i speaking of total stress as load, others have used it for total stress
r!|?' only, calling unit stress intensity of stress. It has therefore been
deemed advisable in this book to firstly use the word for state of
stress in a general sense, and afterwards to speak more par-
ticularly of stress per square inch, and of total stress.
P. 407. Value of w", or the space between rivets in a
single-riveted lap joint, as deduced from the formula at head of
p. 407, depends on the material of the rivet and plate. Assuming
safe stresses as follows: